fuel

My 454 has a pressure regulator on the frame near the fuel tank.

You can see a picture HERE.

Could there be a problem going on in this part?

It might be the mylar sock (filter) on the suction pipe in the rule tank is becoming clogged after it sits for awhile the debris float away and the pump will work again. Might have to pull the tank and clean it out

A leak in the suction side of the pump?

I'm thinking "sock" too, and wondering if there's a plugged vent creating vacuum in the tank. I'm familiar with FORD's of that era. They had in-tank electric pumps that worked on the "Archimedes Screw" principle. That design would allow an external pump to pull fuel through. When Ford went to fuel injection, the pumps changed to a Vane-Type and a failed pump had to be replaced. Or removed and replaced with tubing to use an external pump.
Also, many OP's here with external pumps on Ford's have found they don't last all that long. Again, you're working on a Chevy so I don't know how much of this applies, but I hope it helps.

Sounds like a tank venting problem. See if everything works with the gas cap removed. If so replace the cap.

Matthew,

Have you tried opening the fuel tank cap?
This is an issue that is not uncommon with that period GM vehicles. There was a problem with the purge canister valving.

Note, If you include some breaks and punctuation, it makes it much easier to read. Even if you are working form a small device, breaks alone can help to separate the thoughts.

Matt